9 January 1998

Gas keeps grain pest free

Grain pest control is the

theme of our latest article

gauging reactions of end

users to levy-funded

research presentations.

Andrew Blake reports

NEW ways to use and preserve the life of one of the few remaining storage fumigants are the subject of ongoing research at the Central Science Laboratory.

The use of phosphine gas to kill grain store pests has long been viewed as a last resort, fire-brigade treatment. But with millers, maltsters and other buyers increasingly wary of accepting grain which may contain traces of organophosphorus insecticides, phosphine fumigation which leaves no harmful residues is a valuable alternative, maintains Mark Braithwaite of specialist contractor Igrox.

Recently the firm has begun promoting phosphine for preventative as well as curative treatments.

Until now application has involved solid aluminium phosphide to generate the gas (Arable July 12, 1996). Earlier HGCA-backed research led to a cylinder-based form of phosphine using carbon dioxide as diluent to avoid risk of explosion. This allowed the fumigant flow to be regulated as required.

The latest three-year research project, funded by £50,000/year of HGCA levies, offers more flexibility, which could improve the firms service and cut costs.

The key is having the phosphine immediately available as the gas, explains CSL researcher Chris Bell. For tablets to work effectively at UK temperatures, grain bulks have to be well sealed for at least eight days. But gas containment can be tricky.

"It is quite apparent that in the majority of structures in the UK you can never get a 100% seal," says Dr Bell.

"So our strategy was to look at ways of re-dosing or using continuous dosing. If you can continually feed in gas you have a good chance of keeping enough there for long enough to do the job."

Used in grain bins the concept was initially successful. "It worked very well until you got very big temperature fluctuations, for example with hard frost followed by warm days." This caused a chimney effect which sucked gas out of the bins and increased treatment time, he explains.

"So we then looked at ways of compensating for this." The latest work has developed an automated system of dosing lines with sensors to detect when the phosphine concentration drops. Solenoid valves linked to the sensors automatically feed in more gas as needed. The system, suitable for both silos and floor stores, also offsets the effect of high winds which draw the gas out of buildings.

Taken off quickly

Cost of the auto-monitoring and dosing control unit should be well under £2000, Dr Bell believes. But for the moment lack of registration for the cylinder form of phosphine prevents UK commercial uptake. However a similar idea has taken off quickly in Australia, and fast track approval for the gas is expected in the US by April, he notes.

Ideas to optimise pipework layouts for floor stores are the subject of a new research proposal to HGCA, he adds.

Igrox has agreed to pursue UK registration on behalf of manufacturer BOC, notes Mr Braith-waite.

Using phosphine fumigation to keep grain free of pests and free of pesticide residues looks an increasingly attractive option, say Chris Bell (left), Barry Froggatt (centre) and Ian Clayton Bailey.

Cost of phosphine treatment could fall once BOC sees a secure market for the gas, says Igroxs Mark Braithwaite.